The present invention relates to a process for producing a modified polymer, a modified polymer obtained by the process and a rubber composition. More specifically, the present invention relates to a process for producing a modified polymer which enhances interactions with silica and carbon black when used for both of silica-blended and carbon black-blended rubber compositions and which elevates the fracture characteristic, the abrasion resistance and the low heat buildup property at the same time and can exhibit a good workability, a modified polymer having the characteristics described above which is obtained by the above process, a rubber composition comprising the above modified polymer and a tire prepared by using the above rubber composition.